CONSTITUTION, CONFIGURATION, AND THE OPTICAL-ACTIVITY OF CHIRAL DENDRIMERS

Three series of zeroth to second generation chiral dendrimers, 7-9, 10 -12, and 13-15, were prepared by convergent methods using chiral, nonr acemic AB(2) monomers 1, 2, and 3, respectively. Chiroptical data reve aled a significant change in molar rotation per subunit ([Phi](D)/n) a s dendrimer generation increased for dendrimers 7-9 and 10-12, but not for dendrimers 13-15, a possible indication of chiral conformational order in the former two series of dendrimers, but not in the last. How ever, the optical activities ([Phi](D)) of low-molecular-weight model compounds 16 (+262) and 17 (+122), prepared to simulate different regi ons of the dendrimer structure, suggest that as generation size increa ses slight constitutional changes have a strong effect on the chiropti cal properties of the dendrimer subunits. Using the [Phi](D) values of these and other (18-23) low-molecular-weight model compounds, we calc ulated [Phi](D) values for dendrimers 7-15 that agree within 14% of th e observed values. Agreement between the optical activity of the model compounds and the dendrimers leads to the conclusion that the conform ational equilibria of the dendrimer subunits are not perturbed relativ e to those of the model compounds. Therefore, we interpreted the chang e in [Phi](D)/n as dendrimer generation increased for dendrimers 7-12 to be based solely on constitutional changes in the dendritic structur e and not chiral conformational order.